Hydrothermal Conversion of Neutral Sulfite Semi-Chemical Red Liquor into Hydrochar

Ramy Gamgoum,Yi Chiang,Rafael Santos,Animesh Dutta

doi:10.3390/en9060435

Abstract

Hydrochar was produced from neutral sulfite semi-chemical (NSSC) red liquor as a possible bio-based solid fuel for use in power generation facilities. Hydrothermal conversion (HTC) experiments were conducted using a fixed liquor-to-water volume ratio of 1:8 and reaction time of 3 h. Solutions were processed using different chemical additives, pH and temperature conditions to determine the optimum conditions required for producing a high energy content solid fuel. The hydrochar samples produced were analyzed by ultimate, thermogravimetric (TGA) and Fourier transform infrared spectroscopy (FTIR) analyses to determine physicochemical properties that are important for utilization as a fuel. The residual process liquids were also analyzed to better understand the effect of HTC process conditions on their properties. It was determined that the optimum conditions for producing a solid fuel was at a reaction temperature of 250 °C, in the presence of acetic acid at pH 3. The maximum energy content (HHV) of the hydrochar produced from red liquor at this condition was 29.87 MJ/kg, and its ash content was 1.12 wt.%. This result reflects the effect of increasing reaction temperature on the physicochemical characteristics of the hydrochar. The increase of HTC temperature significantly reduces the ash content of the hydrochar, leads to a significant increase in the carbon content of the hydrochar, and a reduction in both the oxygen and hydrogen content. These effects suggests an increase in the degree of condensation of the hydrochar products, and consequently the formation of a high energy content material. Based on TGA and FTIR analyses, hydrochars prepared at high HTC temperature showed lower adsorbed moisture, hemicellulose and cellulose contents, with enrichment in content of higher temperature volatiles, such as lignin.

Highlights

The changing climate and the increasing demand for clean energy are drivers in the exploration of reliable, low cost, sustainable and environmentally friendly routes to produce fuel materials that can be commercialized
Hydrothermal conversion (HTC) experiments were conducted with neutral sulfite semi-chemical (NSSC) red liquor and deionized water in a batch 1 L
Of NSSC red liquor and 600 mL of deionized water were added to the reactor

Summary

Introduction

The changing climate and the increasing demand for clean energy are drivers in the exploration of reliable, low cost, sustainable and environmentally friendly routes to produce fuel materials that can be commercialized. In 2014, world energy supply, by source and in decreasing order of contribution, originated from: oil 33.6%, coal 26.6%, natural gas 21.5%, biomass and waste 9.5%, nuclear 4.7%, hydro 2.3% and other renewables (solar, wind, geothermal, etc.) 1.8% [1]. Oil, coal and natural gas are the most used energy. Energies 2016, 9, 435 fuels, but their use must be curbed—in order to resolve the escalating issues of global warming and the need for low-carbon fuels, it is essential to increase the adoption of renewable resources. Biomass has recently reemerged as a key piece in the world’s energy mix. Biomass is a renewable energy source derived from living organic matter such as wood, wood waste and agricultural residues

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